The invention relates to a method of charging metal carriers, in particular sponge iron, which contain a portion of fines and are at least partially reduced to a melter gasifier in which a melt-down gasifying zone formed by a bed is maintained, wherein the metal carriers and carbon carriers are fed into the melter gasifier above the level of the melt-down gasifying zone and descend to the melt-down gasifying zone and travel through the same forming a metal melt, in particular forming a pig iron melt, and producing a reducing gas by coal gasification, as well as to a plant for carrying out the method.
From EP-B - 0 010 627 it is known to feed in particulate iron-containing material, such as pre-reduced sponge iron, through a centrally arranged charging opening in the hood of the melter gasifier from above, with the particles dropping into the melter gasifier by the action of gravity and being slowed down in the fluidized bed present within the melter gasifier. Coal in lumpy form is charged through a charging opening arranged laterally in the hood of the melter gasifier or in the dome terminating the melter gasifier toward the top, also under the influence of gravity. The reducing gas formed in the melter gasifier is withdrawn through the centrally arranged charging opening for the iron-containing material.
A process of this kind is not suitable for processing fine-particle metal carriers, in particular fine-particle sponge iron, since the fine-particle metal carriers due to the pronounced gas flow of the reducing gas formed in the melt-down gasifying zone and withdrawn through the central charging opening arranged in the hood or in the dome of the melter gasifier would be instantly carried out of the melter gasifier. Such a discharge of the fine-particle metal carriers is further favored by the temperature prevailing in the upper region of the melter gasifier, i.e. in the region above the melt-down gasifying zone, which is too low to ensure a melt-down, i.e. agglomeration of the fine particles at the charging site to form bigger particles which in spite of the ascending gas stream could sink down into the melt-down gasifying zone.
From EP-A - 0 217 331 it is known to introduce pre-reduced fine ore into a melter gasifier and to completely reduce and melt it by means of a plasma burner while supplying a carbon-containing reducing agent. The pre-reduced fine ore or the sponge-iron powder respectively is fed to a plasma burner provided in the lower section of the melter gasifier. A disadvantage of this method is that by feeding the pre-reduced fine ore directly in the lower meltdown region, i.e. in the region where the melt collects, complete reduction can no longer be ensured and the chemical composition necessary for further processing the pig iron cannot be achieved by any means. Moreover, the charging of large amounts of pre-reduced fine ore is not feasible, on account of the fluidized bed or the fixed bed forming from coal in the lower region of the melter gasifier, as it is not possible to carry off a sufficient quantity of the melting products from the high-temperature zone of the plasma burner. The charging of major amounts of pre-reduced fine ore would lead to instant thermal and mechanical failure of the plasma burner.
From EP-B - 0 11 1176 it is known to feed a fine grain fraction of sponge iron particles into the melter gasifier through a downpipe projecting from the head of the melter gasifier into the proximity of the coal fluidized bed. At the end of the downpipe a baffle plate is provided for minimizing the velocity of the fine grain fraction, resulting in a very low exit velocity of the fine grain fraction from the downpipe. At the charging site, the temperature reigning in the melter gasifier is very low, whereby immediate melting of the supplied fine grain fraction is prevented. This and the low exit velocity from the downpipe cause a substantial portion of the supplied fine grain fraction to be carried out of the melter gasifier again together with the reducing gas generated in the same. The charging of a major amount of sponge iron particles containing a fine portion or of only a fine grain fraction is not feasible in accordance with this method.
From EP-A - 0 594 557 it is known to charge a fine grain fraction of sponge iron by means of a conveying gas directly into the fluidized bed formed by the melt-down gasifying zone in the melter gasifier. However, this is disadvantageous, since hereby the gas-circulation of the fluidized bed may be disturbed because obstructions of the fluidized bed, which acts like a filter, may ensue as a consequence of the fine grain fraction that is blown directly into the fluidized bed. As a result, eruptive outbreaks of gas may occur which will break up the clogged fluidized bed. Hereby, the gasification process for the carbon carriers and also the melt-down process for the reduced iron ore are markedly disturbed.
From EP-A - 0 576 414 it is known to feed fine-particle metal carriers to the melt-down gasifying zone via dust burners. One disadvantage associated with this process is that there may result regions with an excess of metal and regions with an excess of carbon in the melt-down gasifying zone.
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a method of the initially described kind and a plant for carrying out the method, with said method and plant allowing processing of fine-particulate metal carriers without the need of briquetting and wherein, on the one hand, discharge of the supplied fine particles in the pre-reduced or in the completely reduced state by the reducing gas generated in the melter gasifier is reliably avoided and on the other hand, if necessary, a final reduction of the fine particles is ensured. The necessity of separating the metal carriers into a coarse- and a fine-grain fraction is to be avoided. A further object to be achieved in accordance with the invention is to attain a distribution as uniform as possible of the metal carriers and the carbon carriers in the bed of the melt-down gasifying zone.
In accordance with the invention, this object is achieved in that at a vertical distance below a dome terminating the melter gasifier toward the top the metal carriers are fed into the interior of the melter gasifier gravitationally and under the formation of a strand and that the strand is surrounded by a gas jacket enclosing and accompanying the freely falling strand from its level of origin onwards over a section of the fall, and that in this section the strand is supported against expansion by the gas jacket.
Due to the fact that in accordance with the invention the strand is enclosed by a gas jacket supporting the strand, the device that charges the metal carriers into the interior of the melter gasifier, f.i. a downpipe, can be kept short, so that the metal carriers are kept compact over a longer range. By this method, discharge of finer particles of the metal carriers is strongly reduced although the downpipe can be kept short. This also offers the additional advantage of a slight mechanical load on the downpipe, resulting in a high stability of the same.
In accordance with a preferred procedure, the gas jacket is formed by a cooling gas which under the formation of a cooling jacket surrounds a downpipe conducting the metal carriers into the interior of the melter gasifier. Hereby, the gas forming the gas jacket is utilized doubly, namely on the one hand as a cooling gas for the downpipe and on the other hand as a protective jacket forming an extension of the downpipe.
Due to the formation of a cooling jacket for the downpipe it is feasible to utilize commercial high-temperature steels for the downpipe in spite of the high temperatures above the meltdown-gasifying zone, i.e. in the region of the dome that terminates the melter gasifier toward the top. It is in fact known from EP-B - 0 111 176 to provide a downpipe in a melter gasifier, with said downpipe projecting into the melter gasifier from the top to closely above the upper limit of the fluidized bed formed from coal within the melter gasifier, and to provide it with a water cooling. However, such a water cooling constitutes a high safety risk, since water intake into the melter gasifier may lead to the formation of oxyhydrogen gas and hence to explosions.
Preferably, the level of origin of the strand is fixed in a region of the melter gasifier where the maximum velocity of the reducing gas is 0.45 to 0.5 m/s. Hereby, the means for charging the metal carriers to the melter gasifier, f.i. the downpipe, can be kept short and the amount of gas consumed in forming the gas jacket can be kept low.
Preferably, the gas jacket supports the strand against expansion over a section of the height of fall in that the maximum velocity of the reducing gas is 0.2 to 0.3 m/s, thereby minimizing discharge of the fine particles of the metal carriers.
To attain a good supporting effect of the gas jacket, the gas jacket is suitably formed by a gas which flows downward and parallel to the strand and which has a velocity of flow more than ten times, preferably more than fifty times the maximum velocity of the reducing gas in the interior of the melter gasifier.
Utilizing gas from the process itself to serve as the cooling gas and for forming the gas jacket is not only economical but also prevents a change in the composition of the gas in the melter gasifier that would affect the melting-gasifying process.
A plant for carrying out the method, comprising a melter gasifier which has feed ducts for oxygen-containing gases and carbon carriers and at least partially reduced metal carriers and from which a gas discharge duct for a reducing gas departs in the region of a dome terminating the melter gasifier toward the top, and which is provided with a tap for a metal melt, in particular for pig iron and slag, is characterized in that in a dome terminating the melter gasifier toward the top, at a radial distance from at least one gas discharge duct for reducing gas, at least one feed duct with a charging unit for at least partially reduced metal carriers is provided, equipped with a downpipe ending at a distance below the wall that forms the dome, wherein said downpipe is provided with a gas supply means for the generation of a gas jacket forming at the lower end of the downpipe.
Preferably, the downpipe comprises a double jacket defining an annular gap cavity and the gas supply means opens into said annular gap cavity.
For the formation of the gas jacket, the lower end of the downpipe suitably is provided with an annular gap opening or several openings for the exit of a gas flowing through the annular gap cavity.
To attain a distribution as uniform as possible of the metal carriers in the fluidized bed it is of advantage if a plurality of downpipes is arranged at the dome of the melter gasifier, preferably is disposed in a radially symmetrical arrangement.
The invention is in particular suited to a plant for the production of metal melts, in particular pig iron, from charging substances formed of ore, in particular iron ore, and of fluxes and at least partially containing a portion of fines, which is characterized
by at least two fluidized bed reactors subsequently connected in series, wherein the ore is conducted from fluidized bed reactor to fluidized bed reactor via conveying ducts in one direction and reducing gas is conducted from fluidized bed reactor to fluidized bed reactor via reducing-gas connecting ducts in the opposite direction, and
by a melter gasifier into which there runs a feed duct conducting the reduction product from the fluidized bed reactor arranged last in the direction of the ore flow and whose gas discharge duct runs into the fluidized bed reactor arranged last in the direction of the ore flow.